British Columbia Mine Reclamation Symposium

Evaluating differences in tree and shrub performance, soil moisture regime and predicted site series between 50-cm and 100-cm overburden cover depths at Gibraltar Mine Nickels, M.; O'Hara, S.; Straker, J.


Reclamation cover depth influences the plant-available water a given surface material is able to store, which ultimately determines the soil moisture regime (SMR) of a site and its ability to support specific vegetation communities and ecosystems. In 2009, Gibraltar Mine established an overburden-depth trial on the flat top of a waste-rock dump to evaluate tree and shrub performance in overburden-cover depths of 50 cm and 100 cm. Seedlings were planted in 2009 and 2010, and mortality surveys were conducted in 2011 and 2012 to determine initial establishment success of planted species. In 2020, we measured and compared substrate properties, survival and success of planted species, and ecosystem characteristics between the two treatments. We also conducted destructive root-excavation sampling to assess how rooting activity was affected by overburden-cover depths for the two dominant planted species: aspen and black cottonwood. Results indicated the following: • The 100-cm treatment is capable of storing more soil water than the 50-cm treatment, resulting in a mesic SMR compared to the drier submesic SMR in the 50-cm treatment. • Trembling aspen (Populus tremuloides) were significantly taller in the 100-cm than in the 50-cm treatment while no differences were observed in black cottonwood (Populus trichocarpa) or birch (Betula papyrifera), suggesting that aspen can respond more readily to greater water availability. • Poplar-willow-borer attack was more frequent and more severe in aspen and willow (Salix spp.) growing in the 50-cm treatment, which may indicate an increased susceptibility to insect and pathogen attack in shallower cover depths for some species. These results show that using a 100-cm cover depth in reclamation is beneficial for soil water storage, and plant health and growth for some species, relative to using a 50-cm cover depth, and that different depths can be used to create differing conditions for target reclamation ecosystems.

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